Presence Of Other Ions Research Articles

Adsorption behavior and mechanism of NH2-MIL-101(Cr)@COFs@SA composite adsorbent for tetracycline removal

Herein, we employed a rational approach to develop a hydrogel composite material by encapsulating NH2-MIL-101(Cr)/covalent organic frameworks (COFs) in sodium alginate (SA) to effectively capture of tetracycline (TC). Experimental tests and various characterizations (including Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron spectroscopy (SEM), Brunauer-Emmett-Teller (BET), and X-ray photoelectron spectroscopy (XPS)) confirmed that the NH2-MIL-101(Cr)@COFs@SA composite exhibited a more robust, multilayer pore structure with abundant active functional groups. Under conditions of 298 K and pH = 7, the NH2-MIL-101(Cr)@COFs@SA adsorbent demonstrated remarkable TC adsorption capability, achieving a removal rate of 96.38 % in 120 min and a qmax of 252.6 mg/g at 298 K by Langmuir model. Kinetic analysis indicated that the interaction between TC and NH2-MIL-101(Cr)@COFs@SA follows a pseudo-second-order model, suggesting that chemisoption governs the process. The Langmuir model and thermodynamic analysis suggested that TC adsorption follows a monolayer sorption pattern and is spontaneous and exothermic. Even in the presence of other ions, NH2-MIL-101(Cr)@COFs@SA maintained high efficiency for TC adsorption, demonstrating superior selectivity. NH2-MIL-101(Cr)@COFs@SA demonstrated remarkable recyclability, with only a minimal reduction in the removal efficiency (85.5 % and 142 mg/g) after 10 cycles of adsorption and regeneration. Various analytical techniques, including FTIR spectroscopy, SEM, EDX, XPS, and density functional theory (DFT) calculations of adsorption energy were used to elucidate the TC adsorption mechanisms by NH2-MIL-101(Cr)@COFs@SA. The adsorption process primarily involved π-π stacking, hydrogen bonding, electrostatic interactions, and complexation.

Electrochemical detection of quercetin at a Pt nanoaggregate-decorated Ti3C2-modified electrode

The surface chemical state of the electrode modification material, particularly crystal defects, significantly affects electrochemical detection properties. In this study, Ti3C2 decorated by Pt nanoaggregates (Pt NAs-Ti3C2) with enhanced crystal defect was developed for quercetin detection, where Pt nanoaggregates on Ti3C2 exhibit improved dispersibility and smaller particle size, generating a more favorable environment for interfacial catalytic reactions. A large specific surface area, the Pt NAs-Ti3C2 composite is beneficial for the adsorption and transfer of quercetin on the electrode surface. In comparison to Pt nanoaggregates with complete crystals, the Pt NA-Ti3C2-modified glassy carbon electrode (Pt NA-Ti3C2/GCE) demonstrates superior quercetin detection capabilities, achieving a detection sensitivity of 72.3 μA μM−1 and an outstanding detection linear region of 0.1–1500 nM. Besides, the electrode showcases excellent reproducibility with RSD of 2.41 %, repeatability with RSD of 1.08 %, and long-term stability with 92.3 % of the original signal retained, and resistance to interference, achieving accurately and selectively quercetin detection even in the presence of other ions and compounds. In addition, the Pt NA-Ti3C2/GCE allows for precise quercetin detection in real-life samples. Our findings establish a theoretical guideline and furnish the material foundation for the development of high-performance electrochemical sensors.

Effect of operating variables on selective radiostrontium separation from aqueous waste matrices using a novel crown ether-based amino-modified mesoporous silica sorbent

A new sorbent, DFDB18C6@SBA-NH2, created by grafting diformal dibenzo-18-crown-6-ether (DFDB18C6) onto amino-modified mesoporous silica (SBA-NH2) has been used for the selective removal of radiostrontium (r-Sr: 90Sr) from aqueous waste. The Sr-sorption behavior was investigated at various operating conditions, including pH, contact time, initial Sr2+ concentration, temperature, and the presence of competing ions (e.g., Li, Na, K, Rb, Ca, Mg, and Ba). Kinetic investigations showed that the sorption process followed pseudo-second order kinetics, whereas isotherm modeling demonstrated that the Langmuir model provided the most excellent fit, implying monolayer sorption. The thermodynamic study indicated that the sorption process is endothermic. The sorbent effectively removed 90Sr (∼99.67 %) from Chornobyl-derived radioactive wastewater in the presence of other ions. These findings suggest the potential of DFDB18C6@SBA-NH2 as an effective tool for 90Sr separation from aqueous waste matrices.

Detection of Salt Content in Canned Tuna by Impedance Spectroscopy: A Feasibility Study for Distinguishing Salt Levels.

The electrical impedance of dilute aqueous solutions containing extracts from five brands of canned tuna is analyzed using impedance spectroscopy in order to analyze their salt content and detect the potential presence of other salts beyond the well-stated NaCl. A complex electrical impedance is modeled with an equivalent electrical circuit, demonstrating good agreement with experimental data. This circuit accounts for the contribution of ions in the bulk solution, as well as those contributing to electrode polarization. The parameters describing the equivalent circuits, obtained through fitting data to the electrical impedance, are discussed in terms of the various ion contributions to both the electrical double layer at the electrode interface and the electrical conductivity of each solution. The ionic contribution to the electrical impedance is compared with that of a pure NaCl solution at the same concentration range. This comparison, when extended to real samples, allows for the development of a model to estimate the electrical conductivity of canned tuna samples, thereby determining the salt concentration in tuna. The model enables differentiation among the various samples of tuna studied. Subsequently, the potential presence of other ions besides Na+ and Cl- and their contribution to the electrical properties of each canned tuna extract is considered, especially for samples with a higher ratio of the sum of K+ and phosphates to Na+ concentration. This analysis shows the potential of impedance spectroscopy for on-site and rapid analysis of salt content and/or detection of additives in canned tuna fish.

The 8-17 DNAzyme can operate in a single active structure regardless of metal ion cofactor

DNAzymes – synthetic enzymes made of DNA — have long attracted attention as RNA-targeting therapeutic agents. Yet, as of now, no DNAzyme-based drug has been approved, partially due to our lacking understanding of their molecular mode of action. In this work we report the solution structure of 8–17 DNAzyme bound to a Zn2+ ion solved through NMR spectroscopy. Surprisingly, it turned out to be very similar to the previously solved Pb2+-bound form (catalytic domain RMSD = 1.28 Å), despite a long-standing literature consensus that Pb2+ recruits a different DNAzyme fold than other metal ion cofactors. Our follow-up NMR investigations in the presence of other ions — Mg2+, Na+, and Pb2+ – suggest that at DNAzyme concentrations used in NMR all these ions induce a similar tertiary fold. Based on these findings, we propose a model for 8–17 DNAzyme interactions with metal ions postulating the existence of only a single catalytically-active structure, yet populated to a different extent depending on the metal ion cofactor. Our results provide structural information on the 8-17 DNAzyme in presence of non-Pb2+ cofactors, including the biologically relevant Mg2+ ion.

The Elimination of Levofloxacin from High-Salinity Wastewater via the Electrochlorination Process

The electrochlorination (E-Cl) process has attracted much attention as it is a highly efficient method for treating organic compounds in hypersaline wastewater. In this study, the E-Cl process was utilized for the removal of antibiotics. The optimal experimental conditions were determined to be a NaCl concentration of 100 mM, a current density of 1.5 mA/cm2, a pH of 7.0, and a plate spacing of 1 cm, with a levofloxacin (LEV) degradation efficiency reaching as high as 99% using this setup. The effects of the presence of other ions and humic acid on the E-Cl process were investigated, and it was found that the degradation of LEV was not significantly affected by the presence of coexisting substances. In addition, free chlorine was identified as the primary active species for the degradation of LEV by means of a quenching experiment. It was demonstrated by 3D EEM and TOC that LEV was not completely mineralized and that intermediate products may be present. In order to reveal the degradation pathways of LEV, its degradation products were also analyzed via LC-MS, and some possible pathways of LEV degradation in this system were proposed. The successful degradation of LEV demonstrated that the E-Cl process is an efficient and promising technique for the treatment of organic pollutants in high-salinity wastewater.

Combined DFT and ionic model computational study of the effect of alkali metal cations on the structure, bonding and properties of molten cryolites, M3AlF6 (M = li, Na, K, Rb, and Cs)

ABSTRACT Ionic melts, in the form of ionic liquids and molten salts, are important in many technological aspects such as metal production and energy applications. Cryolite melts constitute an important family especially for the industrial production of Al. The present computational study aims to analyse the effect of different cations on the structure and properties of Al (III) fluorocomplexes in cryolite melts. Cation effects are discussed as the ion pair interactions due to alkali metal cations of cryolite compounds M3AlF6 with M= Li, Na, K, Rb, or Cs for various microclusters using ionic interaction model (IM) and DFT calculations. DFT results for different ion complexes are compared with the energy calculations using a pseudoclassical model for isolated clusters. QTAIM and ELF analyses were performed to understand the nature of interactions in detail. A link between open-shell interactions and decreased ionic conductivity is proposed within the series of K, Rb, and Cs. Environmental effects, such as temperature and presence of other ions, are investigated in detail by DFT analysis.

Effect of PFDS on the immobilization of Cs+ by metakaolin-based geopolymers in complex environments

Metakaolin-based geopolymers are very promising materials for improving the safety of low and intermediate level radioactive waste disposal, with respect to ordinary Portland cement, due to their excellent immobilization performance for Cs+ and superior chemical stability. However, their application is limited by the fact that the leaching behavior of Cs+ is susceptible to the presence of other ions in the environment. Here, we propose a way to modify a geopolymer using perfluorodecyltriethoxysilane (PDFS), successfully reducing the leaching rate of Cs+ in the presence of multiple competitive cations due to blocking the diffusion of water. The leachability index of the modified samples in deionized water and highly concentrated saline water reached 11.0 and 8.0, respectively. The reaction mechanism between PDFS and geopolymers was systematically investigated by characterizing the microstructure and chemical bonding of the material. This work provides a facile and successful approach to improve the immobilization of Cs ions by geopolymers in real complex environments, and it could be extended to further improve the reliability of geopolymers used in a range of applications.

Adsorptive Elimination of a Cationic Dye and a Hg (II)-Containing Antiseptic from Simulated Wastewater Using a Metal Organic Framework.

Several types of pollutants have acute adverse effects on living bodies, and the effective removal of these pollutants remains a challenge. Safranin O (a biological dye) and merbromin (a topical mercury-containing antiseptic) are considered organic pollutants, and there are only a few reports on their removal. Synthesized and well-characterized (through PXRD, FTIR, FESEM, and EDS analysis) MOF-5 was used for the first time in the removal of safranin O and merbromin from simulated wastewater and real wastewater. In both cases, MOF-5 effectively removed contaminants. We found that in simulated wastewater, the highest efficiency of removal of safranin O was 53.27% (for 15 mg/L) at pH 10, and for merbromin, it was 41.49% (for 25 mg/L) at pH 6. In the case of real wastewater containing natural ions (Na+, K+, F-, Cl-, SO42-, PO43-, Mg2+, and Ca2+) and other molecules, the removal efficiencies of these two dyes decreased (34.00% and 26.28% for safranin O and merbromin, respectively) because of the presence of other ions and molecules. A plausible mechanism for the removal of these pollutants using MOF-5 was proposed.

Influence of terephthalate anion in ZnAl layered double hydroxide on lead ion removal: Adsorption, kinetics, thermodynamics and mechanism

In this work, layered double hydroxides (LDHs) intercalated with carbonate (ZnAl-CO3) and terephthalate (ZnAl-TA) anions were synthesized for the removal of lead (Pb2+) ions from aqueous solutions. ZnAl-TA showed better Pb2+ removal performance than ZnAl-CO3. In the kinetic study, the Elovich model obtained the best fit; the Weber-Morris model showed that intraparticle diffusion is not a limiting step in the process. The Sips model fitted better to the adsorption isotherms, with a maximum adsorption capacity of 124 mg.g−1. The thermodynamic study showed that the process is spontaneous and endothermic. In the regeneration of ZnAl-TA, the use of NaCl as a desorption eluent showed less Zn2+ leaching and greater desorption efficiency compared to acid eluents. The adsorption capacity of Pb2+ in the presence of other ions followed the order Ni2+ > Ca2+ > Cd2+ > Mg2+ > Cu2+. The ZnAl-TA adsorbent reached 88% of its initial efficiency after 3 cycles with high stability. From post-adsorption XRD, FTIR, and XPS analyses, Pb2+ was removed predominantly by chelation, surface complexation, and precipitation. In general, the ZnAl-TA adsorbent proved to be an efficient sorbent material for Pb2+ removal from aqueous effluent.

Development of a Manganese Dioxide-Decorated Activated Carbon Nano-sorbent via Co-precipitation method for efficient lithium ion adsorption from aqueous solutions

ABSTRACT Recently, the utilization of lithium has increased significantly, particularly in high-tech industries such as nuclear, aerospace, automotive, battery, military, glass and ceramic, and lubricants. However, lithium recovery methods from brines present certain drawbacks, making lithium exploitation a global challenge. A comparative analysis of lithium recovery methods from brine solutions indicates that the adsorption method holds promising potential for separating lithium from low-concentration solutions. Despite this, the quest for an effective and efficient adsorbent for lithium-ion adsorption remains a challenge, necessitating the development of an adsorbent, using readily available materials. In this study, carbon-active underwent chemical modification. Notably, the co-precipitation method was employed for the first time to create a composite adsorbent decorated with manganese dioxide (MnO2). Various analyses, including XRD, SEM-EDS, FTIR, and BET, were conducted to elucidate the structural, morphological, physical, and chemical properties of the adsorbent. This synthesized adsorbent was applied to the adsorption of lithium from an aqueous sample. Exploration of adsorption parameters affecting capacity led to the identification of optimal conditions: 14-hour duration, an adsorbent dosage of 0.02 g, and an ambient temperature of 25°C, in a lithium solution with a concentration of 60.4 ppm. Under these conditions, the maximum adsorption capacity of the adsorbent was determined to be 30.5 mg/g. Based on experimental results, kinetic and adsorption isotherm models were investigated. The Pseudo-quadratic kinetic model, with an R2 value of 0.999, emerged as the most suitable for describing the adsorbent’s behavior. The Hill isotherm model with R2 = 0.9634 is the most appropriate isotherm model to describe the adsorbent behavior. Additionally, the selectivity of the adsorbent in the presence of other ions was investigated. The adsorbent’s reusability was examined, and after two recycling periods, the adsorbent maintained an efficiency of up to 88%, demonstrating its stability. The CAC-MnO2-P composite adsorbent shows technical and economic promise for industrial use in lithium-ion recovery processes.

Hybrid silica nanoparticles functionalized with pyrazolone-tethered organosilane: Synthesis and application for Sn (II) ion sensing in tap water

Pyrazolone tethered triazole functionalized organosilane and their hybrid silica nanoparticles (HSNPs) have been synthesised for the selective detection of Sn(II) using spectrophotometric techniques. The prepared compounds are characterized by FT-IR, NMR (1H and 13C), XRD, mass spectrometry and FE-SEM spectral analyses. The synthesized hybrid silica nanoparticles gave improved detection limit of 4.3 × 10−8 M and stoichiometry of complex between analyte and probe was found to be 1:1. The association constant calculated for organosilane and their HSNPs came out to be 9.54 × 104 M−1 and 7.47 × 104 M−1 while the presence of other ions showed no interference in the sensing behaviour. The results of the use of this sensing system in tap water facilitate its applicability in real samples with the recovery % more than 98.

Design of novel molecular switches using the C20 & C40 nanobud

A molecular switch is a molecule that can reversibly switch between two or more stable states under the influence of environmental factors such as electric current or field, presence of other ions, ligands, pH change, light, etc. Using density functional theory calculations at B3LYP, M06-2X, WB97XD and B3LYP-D3 computational level, we investigate the possibility of using C20 & C40 nanobud as a molecular switch. For this purpose, the effect of different electric fields (0, 0.002, 0025, 0.003, 0.004 and 0.006 a.u.) on structural, electrical and nonlinear optical properties was investigated. It was shown that with the increase of the electric field, the dihedral angle and the bond length of the molecule changes greatly, and a sudden change in the dihedral angle can indicate the switch become ON. Also, with the increase of the electric field, the distance between the HOMO and LUMO orbitals decreases, and this changes increased greatly in a certain range of the electric field, which indicates the change of the state of the molecular switch to ON. The effect of the field on the optical properties of the switch also showed that with the increase in the intensity of the field, the values of α, β and μ increased, and this change was in a specific range of a very strong electric field, which corresponds exactly to the change of the dihedral angle and the behavior of HLG. The M06-2X, WB97XD and B3LYP-D3 methods were used to check the accuracy of the data, and it was shown that the results of these two methods are approximately the same as the results of the calculations related to the B3LYP method.

Extraction of lead in human blood serum using functionalized metal-organic framework-coated glass magnet as adsorbent through stir bar sorptiven extraction

In this work, a glass magnet coated with a thiol-functionalized metal-organic framework was used as an adsorbent to efficiently extract lead ions in the presence of other ions in real samples. One of the most studied face-centred cubic metal-organic frameworks (MOFs) with side pockets and nanoscale channels for film growth is HKUST-1. However, the growth of a thiol-functionalized metal-organic framework (HKUST-1-SH) on a glass magnetic surface as a coating for sorptive stir bar extraction (SBSE) is challenging. HKUST-1 was grown on a glass magnet by liquid phase epitaxy at room temperature. Moreover, a thiol-functionalized metal-organic framework coated on a glass magnet (HKUST-1-SH@Glass Magnet) was successfully synthesized using a simple post-synthesis strategy. The formation of HKUST-1 and HKUST-1-SH on the glass magnetic surface was confirmed and determined by scanning electron microscope images (SEM), energy dispersive X-ray spectrometer (EDS), ATR-IR spectra, and XRD patterns. Some parameters affecting the extraction efficiency, such as pH, extraction time, stirring speed, desorption time, sample volume and elution volume, were studied to improve the sensitivity of the method used. A linear dynamic range of 0.04–30 µg L−1 and a detection limit of 0.005 µg L−1 were obtained under optimal conditions with satisfactory precision and a relative standard deviation of 2.5 % (n = 10, CPb2+ = 15 μg L−1). The extraction efficiency for the determination of lead ions in blood serum samples varied in the range of 95.6 %to 106.2 %.

Separation Performance of Lithium and Calcium from Synthetic Geothermal Brine Using Electric Field-assisted Membrane

Green low-carbon technology development has spurred an increased demand for lithium. Brine, including geothermal brine, is the world’s largest source of lithium. However, the low lithium content and the presence of other ions pose challenges in concentrating lithium. An electric field-assisted membrane is a separation approach combining nanofiltration membranes with an electric field as an additional driving force, effectively separating lithium from magnesium and strontium. This study was conducted to separate lithium and calcium from synthetic geothermal brine using an electric field-assisted membrane. The separation process is conducted for lithium (50 ppm) and calcium (300, 800, and 2,000 ppm) with variations in electrical voltage (0V, 2V, and 3V). The decrease in lithium rejection reaches up to 50% at an electrical voltage of 2V. Conversely, the increase in electrical voltage does not significantly impact calcium rejection (calcium rejection remains at 89% with an electrical voltage of 3V) and the permeate flux for lithium and calcium. The increasing calcium concentration affects permeate flux significantly but does not notably affect calcium rejection, with the rejection remaining above 85%. The findings suggest the feasibility of concentrating lithium through electric field application without compromising calcium rejection within a single salt solution system.

Rapid and selective removal of trace As(III) from water using Fe[sbnd]Mn binary oxide

The rapid removal of trace arsenic is crucial for ensuring the safety of drinking water. However, achieving the rapid removal of trace arsenic poses a significant challenge. In this study, we aim to enhance the removal efficiency of trace arsenic by increasing the specific surface area of the adsorbent material while maintaining its micrometer size. The material design allowed for the rapid removal of trace amounts of As(III) in groundwater within 10 s, resulting in a concentration as low as 0.281 μg L−1, which meets the WHO drinking water standard (<10 μg L−1). Our experimental results demonstrated that the FeMn binary oxide could partially oxidize As(III) into As(V), achieving a removal efficiency exceeding 99 %. Furthermore, we investigated the influence of common cations and anions, such as K+, Mg2+, Ca2+, Cl−, NO3−, SO42−, and PO43−, which may be present in natural water, on As(III) removal. Our findings indicated that the FeMn binary oxide exhibited remarkably high separation factors (ranging from 10 to 103) for other coexisting ions, indicating its exceptional selectivity for As(III) even in the presence of other ions. The outstanding arsenic uptake capability and selectivity of the FeMn binary oxide make it a highly promising adsorbent for the efficient removal of trace As(III) from aqueous solutions.

THE DISSOLUTION OF ANTIMONY OXIDES, AND LEAD AND OTHER RELATED METALS IN ALKALINE-AQUEOUS ORGANIC SOLUTIONS

Metal oxides such as antimony oxide and lead oxide can be dissolved in alkaline-aqueous organic solutions through various methods, including acid-base reactions, complexation, ion exchange, and redox reactions. These methods involve manipulating factors such as pH, temperature, type of solvent, concentration of metal oxide, and presence of other ions. By dissolving metal oxides, they can be extracted from various materials.

Rhodamine Derivative-Linked Silica-Coated Upconverting Nanophosphor (NaYF4: Yb3+/Er3+@SiO2-RBDA) for Ratiometric, Ultrasensitive Chemosensing of Pb2+ Ions

Lead (Pb2+) ions are considered as one of the primary environmental pollutants and have a profound effect on human health. In this work, we have developed a hybrid organic–inorganic optical nanochemosensor for selective and ultrasensitive detection of Pb2+ ions based on energy transfer (ET), involving a Pb2+ sensitive rhodamine-derived named (E)-4-(((3′,6′-bis(diethylamino)-3-oxospiro[isoindoline-1,9′-xanthen]-2-yl)imino)methyl)benzaldehyde represented as RBDA, covalently linked with silica coated upconverting nanophosphors (UCNPs). The UCNPs emit visible light after being excited by NIR light, activating the Pb2+ coordinated RBDA (fluorescent probe). When Pb2+ ions were added, a yellow emission band at about 588 nm formed in upconverting photoluminescence spectra, whereas the strength of green emission at about 542 nm reduced upon excitation of 980 nm laser, indicating the energy transfer from UCNP to RBDA-Pb2+ complex. The concentration of Pb2+ ions directly affects how well the probe reabsorbs the green emission of the nanophosphor, thus enabling the ratiometric chemosensing. With a detection limit of 20 nM in aqueous, the resulting ET-based nochemosensor can also preferentially detect Pb2+ despite the presence of other ions. Owing to the minimal autofluorescence and the great penetration depth of NIR light and special optical features of UCNPs, this is a promising approach for sensitive and in-depth detection of Pb2+ ions in a complex ecological and biological specimen.

Ethylenediamine functionalized waste polyethylene terephthalate-derived metal-organic framework for adsorption of palladium ions from aqueous solutions

The recovery of palladium metal is essential in order to meet its growing global demand and also to address water pollution crisis. Herein, MIL-101(Cr)/ED was fabricated from waste polyethylene terephthalate (PET) bottles and modified using ethylenediamine (ED) to retrieve divalent palladium (Pd(II)) metal ions from aqueous environment. The successful grafting of ED moieties onto MIL-101(Cr) was established by the appearance of broad bands at around 2800–3300 cm−1 on the Fourier transform infrared spectrum which was supported by the increase in binding energy using density functional theory. The adsorption experiments revealed that higher Pd(II) ion intake occurred using 30 mg of MIL-101(Cr)/ED in acidic media of pH = 3.0. The data fit better on the Langmuir isotherm with the correlation coefficient (R2) 0.9089. At 25 °C, the MIL-101(Cr)/ED achieved a substantial enhancement in the intake capacities of 454.2 mg.g−1. Kinetics data demonstrated to comply with pseudo-second order, achieving a rapid rate of Pd(II) adsorption by the MIL-101(Cr)/ED in less than 3 min given by the rate constant k2 = 0.02065 g.mg−1.min−1. The MIL-101(Cr)/ED has high affinity for Pd(II) ions as more than 80% removal was achieved even in presence of other ions. These observations revealed the potential utilization of MIL-101(Cr)/ED as an adsorbent to efficiently extract Pd(II) ions from wastewater.

Competitive Adsorption of Quaternary Metal Ions, Ni2+, Mn2+, Cr6+, and Cd2+, on Acid-Treated Activated Carbon

This paper examined the competitive removal of metal ions from quaternary aqueous solutions containing Ni2+, Mn2+, Cr6+, and Cd2+ using adsorption on both acid-modified and unmodified activated carbon. Activated carbon (AC) was oxidized with nitric acid, both in granular (AGC) and powder (APC) forms, and tested for the competitive adsorption of Ni2+, Mn2+, Cr6+, and Cd2+ from an aqueous solution. Surface oxidation led to a reduction in BET surface area and HK pore width and an increase in the intensities of hydroxyl and carboxyl functional groups for both AGC and APC compared to unmodified activated carbon, AC, as indicated with BET and FTIR analyses. The adsorption capacity of all four metal ions on AC was in the order Ni2+ &gt; Cd2+ &gt; Cr6+ &gt; Mn2+, while it was altered for the two oxidized AGC and APC carbons to be Cr6+ &gt; Ni2+ &gt; Cd2+ &gt; Mn2+. Acid treatment resulted in high selectivity for Cr6+ over all other available ions with a 100% removal efficiency, while it decreased for Ni2+, Cd2+, and Mn2+ compared to AC. This improvement in Cr6+ adsorption is due to its higher ionic potential and smaller size, which results in a faster diffusion and stronger adsorption to the acidic groups located at the pore edges. Therefore, it will repel and hinder other ions from accessing the activated carbon pores. Modeling of the adsorption isotherms with DKR was better than both Freundlich and Langmuir for the competitive ions. DKR showed strong attraction for both Ni2+ and Cd2+ by ion exchange on the AC surface, as indicated by their apparent adsorption energy (E) values. Cr6+ adsorption was found to be by physical adsorption on AC and by ion exchange on both AGC and APC. Mn2+ ions had a very weak attraction to all types of tested activated carbons in the presence of other ions.